MANGANESE IN GOLD DEPOSITS 19 



outcrops of those which do not carry manganese, and whether 

 placers are more frequently developed in connection with non- 

 manganiferous lodes, the reports of Dr. R. W. Raymond 1 have been 

 of great value. 



I wish to acknowledge my indebtedness to my colleagues of 

 the U.S. Geological Survey, and to many other geologists whose 

 accurate observations I have drawn upon to test the hypothesis. 

 Their conclusions respecting the secondary enrichment of gold 

 appear to support the hypothesis, and, differing as they do with 

 respect to the migration of gold in particular deposits, they become 

 reconciled when inspected from this viewpoint, and thus they 

 are themselves supported. Dr. R. C. Wells has read critically 

 certain portions of this paper, where the principles of physical 

 chemistry are involved. 



II. SALTS CONTAINED IN THE WATERS OF GOLD AND SILVER MINES 

 IN NON-CALCAREOUS ROCKS 



Sankowsky and Russell, utilizing all data available to them, 

 recalculated the analyses to the ionic form of statement, and made 

 the general average given in Table I. 



Sulphates.-— Primary gold ores generally carry pyrite, which, 

 oxidizing at or near the surface, yields ferrous sulphate, ferric 

 sulphate, and sulphuric acid. The acid is not formed directly 

 from galena, PbS, or from zinc-blende, ZnS; but pyrite, FeS 2 , 

 carries more sulphur than is required to supply S0 4 to satisfy the 

 iron, even if ferric sulphate, Fe 2 (S0 4 ) 3 , is formed instead of FeS0 4 . 

 As shown by Buehler and Gottschalk, galena and zinc-blende dis- 

 solve much more slowly in the absence of FeS 2 . The reaction 

 probably requires free acid, which the iron sulphide, owing to its 

 excess of sulphur, supplies. The sulphuric acid from pyrite is 

 increased also by the hydrolization of ferric sulphate, and the 

 deposition of limonite. 



In Table I the sulphate radical is nearly ten times as great as 

 -all other negative ions and is also in excess of bases, so that on any 

 basis of adjustment to form salts much H 2 S0 4 remains. The 

 table shows also an average of 97.26 parts per million of hydrogen, 

 indicating the strongly acid character of the solutions. 



1 Mines and Mining West of the Rocky Mountains (1868-75). 



